1. Field of the Invention
The invention relates to a fuel cell system and an operation method for a fuel cell.
2. Description of the Related Art
A fuel cell is generally a device that produces electric energy through the use of hydrogen and oxygen as fuels. The fuel cell, being excellent in terms of environmental quality and capable of realizing high-energy efficiency, has been widely studied and developed as a future energy supply system.
For example, a solid polymer electrolyte fuel cell has a structure in which a catalyst layer and a gas diffusion layer are stacked in that order on both sides of a solid polymer electrolyte membrane that has proton conductivity. At the time of fuel lack in such a solid polymer electrolyte fuel cell, electrolysis of the water produced as a result of electric power generation, occurs at an anode side to produce protons. Due to this electrolysis, protons can be supplied to the electrolyte membrane. However, when the electrolysis of water ceases to progress, there is a risk of degradation of the fuel electrodes due to oxidation. Published Japanese Translation of PCT Application, JP-T-2003-508877, discloses a technology in which a water-electrolytic catalyst is mixed in fuel electrodes. According to this technology, the electrolysis of the power generation-produced water can be accelerated through the water-electrolytic catalyst.
However, water freezes below the freezing point. Therefore, when fuel becomes lacking below the freezing point, there is no water to be electrolyzed. In such a case, water content in the solid polymer electrolyte membrane is extracted to the fuel electrode, and is electrolyzed. In consequence, there is a risk of degradation of the solid polymer electrolyte membrane.